1. Field of Invention
The present invention generally relates to rotating disk type storage devices. The method and apparatus of this invention have particular application to enhancing a disk""s performance.
2. Discussion of Prior Art
Rotating magnetic storage devices typically comprise at least one platter with multiple concentric tracks divided into a plurality of sectors. A read/write head travels across the surface of the platter in response to disk controller commands and positions itself over a sector or group of sectors. Moving a head from the ending of one command to the beginning of the next command is known as a xe2x80x9cseekxe2x80x9d.
The time it takes the head to move from one track to another is usually referred to as seek time. The time it takes for a target sector to rotate until it is positioned under the head is referred to as rotational latency.
Prior art references relating to rotating magnetic storage media recognize that delays due to head positioning, which occur between data storage/retrieval commands, adversely affect throughput rates for disk systems. As seen in the specific patents discussed below, solutions have been proposed to reduce, eliminate or minimize such adverse effects.
In contrast, the present invention does not try to reduce seek time but uses the time between two commands to improve disk performance.
U.S. Pat. No. 4,310,882 issued to Hunter et al., describes a legacy fixed-disk assembly which requires a host system to instruct the disk on basic functions. In such a system, movement commands had a severe overhead penalty which was addressed by holding seek commands until another movement command was received and then executing both commands.
U.S. Pat. No. 5,761,692 issued to Ozden et al., describes a method of re-ordering disk access requests in order to reduce seek time and a method of xe2x80x9croll mode readingxe2x80x9d to avoid rotational latency. However, no teaching of intelligently using rotational latency to improve future read performance is provided by this reference.
DE 19839031, and its equivalent GB 2328780, teach saving power by slowing a disk""s head movement to accommodate both seek time and rotational latency. The head is positioned over a target sector xe2x80x9cjust-in-timexe2x80x9d; however, no intelligent use of the rotational latency period to acquire data is taught.
Whatever the precise merits and features of the prior art in this field, the earlier art does not achieve or fulfill the purposes of the present invention. The prior art does not provide for delaying a seek for a disk access command, based on a rotational latency time period, in order to improve disk performance.
Modern disk drives typically prefetch data to populate a cache. When multiple I/O commands are queued, however, prefetching is usually preempted thereby reducing the data available for cache hits. The present invention calculates the seek-time and rotational latency between successive I/O commands and determines what prefetching can be accomplished without affecting data throughput.